This application relates to multi-link conveyor chains, such as silent or inverted tooth chains, and methods of improving various operating characteristics of conveyor chains. Such chains are frequently used in transporting and conveying materials either as a conveying surface or as the means for moving other containers in which a conveyed material is placed and are commonly used to transport items in a variety of industries. In conveying applications, conveyor chains generally slide on a wear resistant supporting surface with the teeth of the links facing downward, resting on the wear resistant surface. Items to be transported, for example, glass items such as bottles, are placed on the top of the chain. In conveying applications such as described above, the conveyor chain is subjected to wear at the tips of the link teeth where they contact the wear resistant supporting surface. As the chain rotates in its endless path, the tips of the link teeth are gradually worn down, decreasing the overall height of the conveying chain. As the chain height decreases, the accurate and uniform transfer of items onto and off of the top of the conveyor chain can be gradually impaired, resulting in product tipping and mishandling. Eventually, unless repaired or replaced, the conveyor chain height is reduced to the point that the chain is no longer usable.
In current practice, the individual link plates that make up the conveyor chain perform several important functions within the chain, including support of the chain provided by the link tips, control of the chain pitch according to the location and geometry of link apertures, contribution to chain tensile strength dependent on link geometry, and in some instances, guiding of the chain's interaction with sprockets.
In order to reduce the rate of link tip wear and prolong the useful life of the conveyor chain, some manufacturers produce conveyor chains in which every chain link is fabricated from materials having enhanced wear resistance, for example, wear resistant steel alloys. While the use of wear resistant materials for the entire chain may produce the desired reduction in link tip wear, such chains often contain thousands of individual link plates, making the overall chain cost prohibitive. The use of such enhanced wear resistant materials may also complicate the production of a chain with acceptable pitch and adequate tensile strength. Many such materials are difficult to machine or stamp, and the precise location and sizing of link holes needed to control chain pitch can be difficult. Additionally, some wear resistant materials are brittle and may have insufficient toughness or tensile strength, thereby reducing the overall load carrying capacity of the conveyor chain.
The prior art includes inverted tooth conveyor chains that have more than one link design incorporated into the chain. For instance, most conveying chains contain two link designs: conventional tooth shaped driving links and non-toothed guide links. The non-toothed guide links are designed to guide and retain the chain on sprockets during sprocket rotation. The guide links may be included in a chain assembly in single rows or in multiple rows, and these rows may be located on the outer edges of a chain or in the center of the chain. Although these guide links may rest on the wear plate that supports the chain and they may contribute to the support of the chain their intrinsic wear resistance does not differ from the conventional tooth shaped links in the chain. The guide links are manufactured in the same manner as conventional links and have many of the same features. They are stamped from the same steel type and thickness, they undergo the same heat treating, and the geometry and location of the link apertures within the link is the same as conventional links. Thus a chain containing conventional links and guide links is essentially homogeneous with regard to material type, material thickness, heat treatment, and aperture geometry and location.
Other prior art includes conveyor chains that are made with conventional inverted tooth links as well as special “end protector links” positioned only on the outside edges of the chain. These end protector links are designed to prevent the ends of the riveted pins, at the sides of the chain, from damage or wear caused by rubbing of the ends of the riveted pins against guide strips or other lateral obstructions. These end links are not designed to protect the chain from the link tip wear of the type that can cause vertical shifting of the conveyor chain from a nominal operating position over time. Also, since end protector links are located only at the edges of the conveyor chain, they do not restrict link tip wear across the full width of the chain. In chains with end protector links, conventional inverted tooth links in the chain assembly nevertheless rest directly on the conveying support surface, and experience link tip wear during chain operation.
Therefore, the present application discloses a variety of structures intended to prevent or substantially retard wear to a conveyor chain caused by prolonged engagement of chain link tips against a supporting surface.